Anti-Neutrinos May Hold The Key To Solving Physics Mystery

Alex Knapp
,
Forbes Staff
I write about the future of science, technology, and culture.

An international experiment with anti-neutrinos may hold the key to solving one of the great mysteries of physics.

The classic question of cosmology - and, one might say, of philosophy - is "Why is there something rather than nothing?"

Perhaps only slightly behind that question, at least for physicists, is "Why is there matter rather than antimatter?"

Given physics as we understand it, there's no reason for the Universe to exist at all - the Big Bang should have created an equal amount of matter and antimatter. Those particles should have then annihilated each other, leaving nothing but billions of photons and no other kinds of matter. (As though the god of Genesis had said, "Let there be light!" and stopped there.) Since this didn't actually happen (as evidenced by the fact that we're here), physicists have been testing competing theories to explain why the universe is comprised (as far as we can tell) almost entirely of matter rather than antimatter.

Now, though, physicists may have a clue as to where the difference lies. That's thanks to the Daya Bay Reactor Neutrino Experiment, an international collaboration between physicists in China and the U.S., in an experiment taking place at a nuclear reactor in China. The goal of the experiment is to help distinguish the difference between neutrinos and anti-neutrinos.

Both neutrinos and anti-neutrinos oscillate between different states that physicists called "flavors." There are six parameters to the different flavors - three mass states and three mixing angles. (What's behind these states are some very complicated mathematics, which Wikipedia has an overview of here.) All of the parameters were known prior to Daya Bay except one - the third mixing angle of neutrino oscillation. In their measurements, the physicists determined that this mixing angle was 8.8 degrees - give or take .8 degrees.

So why does this matter? Well, the fact that the mixing angle is greater than zero means that neutrinos and anti-neutrinos don't oscillate in the same way. That suggests that it's possible that neutrinos and anti-neutrinos operate using different physical laws. If that's the case, then that provides physicists with a stepping stone for understanding why the universe is mostly made of matter.

"Physicists have put their last hope on the neutrino to explain the absence of anti-matter in the universe," said team member Karsten Heeger in a statement.

Now that the third mixing angle has been established, these physicists and others can start moving on to other experiments to try to ascertain why the mixing angle is what it is. And from there they hope to eventually find a definitive answer to the mystery of matter.

"The neutrino community has been waiting for a long time for this parameter, which will be used for planning experiments for next decade and beyond," said Heeger.

Update: Dr. Heeger offered this clarification in the comments below: "Strictly speaking, the goal of the Daya Bay experiment is not to “help distinguish the difference between neutrinos and anti-neutrinos”. The Daya Bay experiment has only measured the probability of anti-neutrino oscillations between different flavors using the anti-neutrinos from the nuclear power plant. Since we found the mixing angle to be non-zero the next generation of experiments can now go on to determine the possible differences between neutrinos and anti-neutrinos. Measuring a non-zero mixing angle was a pre-requisite."